3-D dimpled heat exchanger

ABSTRACT

A heat exchanger apparatus comprising a frame, a tube coupled to the frame, and turbulating structure disposed within the tube and extending into an inner hollow space thereof for promoting turbulent fluid flow within the tube. The turbulating structure comprises elements located arcuately around an inner periphery of the tube at approximately 120° increments. A method of manufacturing and a heating system is also provided.

TECHNICAL FIELD OF THE INVENTION

The present invention is directed, in general, to heat exchange apparatus and, more specifically, to a design for heat exchanger tubes.

BACKGROUND OF THE INVENTION

Heat exchange tubes are used to transfer heat between two media by using, for example, a so-called “tube-in-tube” design or a “shell-in-tube” design. In a “tube-in-tube” design the fluid product to be heated or cooled flows through a product tube or series of product tubes and the heating or cooling media flows through an outer media tube or series of media tubes usually in a countercurrent fashion with respect to the product flow. Thus, heat is transferred between the media flowing in the inner space between the walls of the media and product tubes and the fluid product flowing through the product tubes or tubes. In a “shell-in-tube” design the product tubes are disposed within a container referred to as a shell and within which the heating or cooling media flows over all of the product tubes from an inlet to an outlet thereof to transfer heat between the media and the product.

To improve heat transfer efficiency the product tubes in either a tube-in-tube design or shell-in-tube design have included turbulating structure of various configurations to promote flow within the tube at a Reynolds number between 8,000 and 10,000, approaching turbulent flow. Generally stated, turbulent flow increases the heat transfer efficiency of the tube by distributing the core fluid flowing therethrough across the entire diameter of the tube and not in streams flowing generally parallel to the axis of the tube in substantially laminar flow. Since a higher rate of heat transfer occurs adjacent the wall of the product tube, ideally a flow pattern is created which eliminates a temperature gradient within the fluid at any cross section taken through the tube.

One method of inducing turbulent flow that has been used with some success is the formation of paired dimples in an outer surface of the heat exchange tube. In many cases, the pairs of dimples are diametrically opposite on the surface of the tube. In some cases, the dimples are co-linear along a line parallel to the axis of the tube. In other cases, successive dimple pairs are non-co-linear, being positioned axially by a set number of degrees, e.g., 30° or 40°, from the previous pair so as to induce an additional rotational effect to the fluid flow.

Nonetheless, there is continual emphasis in most industries to make ever more efficient units in ever more restricted space. This is particularly true in the heating and air conditioning industry where reducing the heat exchanger cabinet size for a given tonnage is always a design objective. As a result, conventional approaches to increasing efficiency and therefore increasing Reynolds number are limited by the geometry of the system.

Accordingly, what is needed in the art is an improved design for turbulating mechanisms in heat exchanger tubes to improve efficiency within a given tube length.

SUMMARY OF THE INVENTION

To address the above-discussed deficiencies of the prior art, the present invention provides a heat exchanger apparatus comprising a frame, a tube coupled to the frame, and turbulating structure disposed within the tube and extending into an inner hollow space thereof for promoting turbulent fluid flow within the tube. The turbulating structure comprises elements located arcuately around an inner periphery of the tube at approximately 120° increments. A method of manufacturing and a heating system is also provided.

The foregoing has outlined preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates a side elevation view of a portion of one embodiment of a heat exchanger tube constructed according to the principles of the present invention;

FIG. 2 illustrates a cross sectional view of the heat exchanger tube of FIG. 1 at plane 2-2;

FIG. 3 illustrates a perspective view of a portion of the heat exchanger tube of FIG. 1;

FIGS. 4A-4C illustrate sectional views of the heat exchanger tube of FIG. 3 at planes 4A-4A, 4B-4B, and 4C-4C, respectively;

FIG. 5 illustrates a side elevation view of a portion of a first alternative embodiment of the heat exchanger tube of FIG. 1;

FIGS. 6A--6C illustrate sectional views of the heat exchanger tube of FIG. 5 at planes 6A-6A, 6B-6B, and 6C-6C, respectively;

FIG. 7 illustrates a side elevation view of a portion of a second alternative embodiment of the heat exchanger tube of FIG. 1;

FIGS. 8A-8C illustrate sectional views of the heat exchanger tube of FIG. 7 at planes 8A-8A, 8B-8B, and 8C-8C, respectively;

FIG. 9 illustrates a side elevation view of a portion of a third alternative embodiment of the heat exchanger tube of FIG. 1;

FIGS. 10A-10C illustrate sectional views of the heat exchanger tube of FIG. 9 at planes 10A-10A, 10B-10B, 10C-10C, respectively;

FIG. 11 illustrates a side elevation view of one embodiment of a heat exchanger tube constructed according to the principles of the present invention;

FIG. 12 illustrates a perspective view of one embodiment of a hydraulic dimpler for the manufacture of a heat exchanger tube constructed according to the principles of the present invention;

FIG. 13 illustrates an enlarged view of the part holder and a portion of the first, second and third hydraulic rams of FIG. 12; and

FIG. 14 illustrates a heating system constructed according to the principles of the present invention.

DETAILED DESCRIPTION

Referring initially to FIG. 1, illustrated is a side elevation view of a portion of one embodiment of a heat exchanger tube 100 constructed according to the principles of the present invention. In a preferred embodiment, the heat exchanger tube 100 comprises a tube 110 having a weld seam 111 along a length l and parallel to a centerline 112 thereof, and a turbulating structure 121 extending into an inner hollow space therein around an inner periphery thereof. In one embodiment, the turbulating structure 121 comprises a plurality of elements 122 a-122 c, 123 a-123 c, 124 a-124 c, in their respective groups 122, 123, 124 of multiple elements disposed at spaced apart intervals i along the length 1 of the tube 110. In a preferred embodiment, the plurality of elements 122 a-122 c, 123 a-123 c, 124 a-124 c comprise a plurality of dimples 122 a-122 c, 123 a-123 c, 124 a-124 c arranged in respective trios 122, 123, 124 wherein centers 125 of each dimple of each trio group 122, 123, 124 are substantially co-planar with a respective plane 132, 133, 134 that is normal to the centerline 112 of the tube 110 and passing through the centers 125. In a preferred embodiment, the dimples 122 a-122 c, 123 a-123 c, 124 a-124 c are smoothly curved surfaces.

Referring now to FIG. 2 with continuing reference to FIG. 1, illustrated is a cross sectional view of the heat exchanger tube 100 of FIG. 1 at plane 2-2. The cross section at plane 2-2 is substantially the same as at planes 132, 133, and 134. In a preferred embodiment, the heat exchanger tube 100 has dimples 225 a-225 c with a depth d spaced at approximately 120° intervals 210 around the inner periphery 213 of the tube 100. The weld seam 111 is diametrically opposed to a center 221 of one 225 c of the dimples 225 a-225 c so as to avoid placing a dimple on the weld seam 111. This orientation of the weld seam 111 reduces the likelihood of stressing the weld seam 111 during forming of the dimples 225 a-225 c or thereafter. One who is of skill in the art will recognize that because three dimples 225 a-225 c are being formed, the depth d of each dimple 225 a-225 c is manifestly less than dimples formed in opposed pairs, therefore, there is less residual stress in the tube 110 as a result of the forming to be described below. Of course, the problems associated with forming a dimple on a weld may be solved by using seamless tubing as will be important in embodiments yet to be described. This becomes increasingly significant as successive dimple sets are displaced radially around the surface of the tubing.

As an example, a reference radius 215 may be drawn from the centerline 112 through a center 221 a-221 c of one 225 a of the dimples 225 a-225 c. The significance of this reference radius 215 will be discussed below. In a typical heat exchanger tube 100 formed from 2 inch tubing and using a 1 inch diameter hemispherical tool end, the dimple depth d can be adjusted up to a maximum dimple depth d of about 0.867″. The dimple depth d and tubing size can be adjusted to achieve a desired Reynolds Number. In a preferred embodiment, internal area of ⅝-inch tubing at the dimples may be sized to produce a Reynolds Number from about 8,000 to about 10,000 with about a 400° F. to about a 450° F. flue temperature. In a like manner, using ½-inch tubing produces a Reynolds Number of about 12,000 under the same conditions. It should be noted that tubing of any appropriate diameter and wall thickness can be used. Also, the dimple depth can be controlled down to the limit wherein a set of dimples touch at the centerline within the tubing. In one embodiment, the first dimple trio 122 may have a first dimple depth and the second dimple trio 123 may have a second dimple depth wherein the second dimple depth is not equal to the first dimple depth. One who is of skill in the art will recognize that this variation of dimple depth may be applied to vary from one set of dimples to the next all along the tubing. Additionally, the diameter of the hemispherical tool end can be increased or decreased in order to change the size of the dimples and correspondingly the Reynolds number. In a preferred embodiment, the heat exchanger tube 100 comprises a path 230 for off-cycle or off-season condensate.

Referring now to FIG. 3, illustrated is a perspective view of a portion of the heat exchanger tube 100 of FIG. 1. In a preferred embodiment, the heat exchanger tube 100 has at least four dimple trios 310, 320, 330, 340 spaced-apart by an interval i. In one embodiment, the interval i is a constant for a given heat exchanger tube 100. In an alternative embodiment, the interval i between successive dimple trios is variable in order to introduce more turbulence in the flow throughout the heat exchanger tube 100. The first dimple trio 310 has a first reference radius 311 drawn from the centerline 112 through a center 312 of one 310 a of the dimples 310 a-310 c in the manner as described with reference to FIG. 2. In a like manner, the second dimple trio 320 has a second reference radius 321 drawn from the centerline 112 through a center 322 of one 320 a of the dimples 320 a-320 c, and the third dimple trio 330 has a third reference radius 331 drawn from the centerline 112 through a center 332 of one 330 a of the dimples 330 a-330 c. In a preferred embodiment, the first, second and third radii 311, 321, 331 are substantially coplanar.

Referring now to FIGS. 4A-4C, illustrated are sectional views of the heat exchanger tube 100 of FIG. 3 at planes 4A-4A, 4B-4B, and 4C-4C, respectively. As can be seen, the reference radii 311, 321, 331 are coaligned, and would therefore be coplanar, i.e., they lie in a common plane defined by the longitudinal axis 112 and the first and third reference radii 311, 331. of course, additional dimple trios with their associated reference radii could likewise be formed in the heat exchanger tube 100 with their associated reference radii in an extension of the same plane.

Referring now to FIG. 5, illustrated is a side elevation view of a portion of a first alternative embodiment 500 of the heat exchanger tube of FIG. 1. The heat exchanger tube 500 comprises first, second and third sections 510, 520, 530, respectively. The first section 510 has a first trio of dimples 511 a-511 c; the second section 520 has a second trio of dimples 521 a-521 c; and the third section 530 has a third trio of dimples 531 a-531 c. In this embodiment, the second trio of dimples 521 a-521 c is clockwise rotationally offset from the first trio of dimples 511 a-511 c about a longitudinal axis 512 by an angle α₁ (See FIG. 6B). The third trio of dimples 531 a-531 c is clockwise rotationally offset from the second trio of dimples 521 a-521 c about the longitudinal axis 512 by an angle α₂ (See FIG. 6C). In a preferred embodiment, the angles α₁ and α₂ may be any number of degrees between about 5° and about 30°.

Referring now to FIGS. 6A-6C with continuing reference to FIG. 5, illustrated are sectional views of the heat exchanger tube 500 of FIG. 5 at planes 6A-6A, 6B-6B, and 6C-6C, respectively. In the illustrated embodiment, the second trio of dimples 521 a-521 c is clockwise rotationally offset from the first trio of dimples 511 a-511 c by an angle α₁. As an example, in the illustrated embodiment, the angle α₁ is about 15°. In a similar manner, the third trio of dimples 531 a-531 c is clockwise rotationally offset from the second trio of dimples 521 a-521 c by an angle α₂. Again, as an example, in the illustrated embodiment, the angle α₂ is also about 15°.

Referring now to FIG. 7, illustrated is a side elevation view of a portion of a second alternative embodiment 700 of the heat exchanger tube of FIG. 1. The heat exchanger tube 700 comprises first, second and third sections 710, 720, 730, respectively. The first section 710 has a first trio of dimples 711 a-711 c; the second section 720 has a second trio of dimples 721 a-721 c; and the third section 730 has a third trio of dimples 731 a-731 c. In this embodiment, the second trio of dimples 721 a-721 c is counterclockwise rotationally offset from the first trio of dimples 711 a-711 c about a longitudinal axis 712 by an angle α₃ (See FIG. 8B). The third trio of dimples 731 a-731 c is counterclockwise rotationally offset from the second trio of dimples 721 a-721 c about the longitudinal axis 712 by an angle α₄ (See FIG. 8C). In a preferred embodiment, the angles α₃ and α₄ may be any number of degrees between about 5° and about 30°.

Referring now to FIGS. 8A-8C with continuing reference to FIG. 7, illustrated are sectional views of the heat exchanger tube 700 of FIG. 7 at planes 8A-8A, 8B-8B, and 8C-8C, respectively. In the illustrated embodiment, the second trio of dimples 721 a-721 c is counterclockwise rotationally offset from the first trio of dimples 711 a-711 c by the angle α₃. As an example, in the illustrated embodiment, the angle α₃ is about −15°. In a similar manner, the third trio of dimples 731 a-731 c is counterclockwise rotationally offset from the second trio of dimples 721 a-721 c by the angle α₄. Again, as an example, in the illustrated embodiment, the angle α₄ is also about −15°. In this alternative embodiment, the rotational offset is counterclockwise by the angles α₃ and α₄. The rotational offset between successive dimple trios may be individually varied between about 5° and about 30°.

Referring now to FIG. 9, illustrated is a side elevation view of a portion of a third alternative embodiment 900 of the heat exchanger tube of FIG. 1. The heat exchanger tube 900 comprises first, second and third sections 910, 920, 930, respectively. The first section 910 has a first trio of dimples 911 a-911 c; the second section 920 has a second trio of dimples 921 a-921 c; and the third section 930 has a third trio of dimples 931 a-931 c. In this embodiment, the second trio of dimples 921 a-921 c is clockwise rotationally offset from the first trio of dimples 911 a-911 c about a longitudinal axis 912 by an angle α₅ (See FIG. 10B). The third trio of dimples 931 a-931 c is counterclockwise rotationally offset from the second trio of dimples 921 a-921 c about the longitudinal axis 912 by an angle α₆ (See FIG. 10C). In a preferred embodiment, the angles α₅ and may be any number of degrees between about 5° and about 30°.

Referring now to FIGS. 10A-10C, illustrated are sectional views of the heat exchanger tube of FIG. 9 at planes 10A-10A, 10B-10B, 10C-10C, respectively. In this embodiment, a second trio of dimples 921 a-921 c is clockwise rotationally offset from a first trio of dimples 911 a-911 c by the angle α₅. As an example, in the illustrated embodiment, the angle α₅ is about 15°. In a similar manner, the third trio of dimples 931 a-931 c is counterclockwise rotationally offset from the second trio of dimples 921 a-921 c by the angle α₆. Again, as an example, in the illustrated embodiment, the angle α₆ is about −30°. In this alternative embodiment, the rotational offset is offset clockwise by the angle α₅ and counterclockwise by the angle α₆. In this embodiment, the rotational offset between successive dimple trios may be individually varied between about 5° and about 30°. In this advantageous embodiment, the rotational offset reverses with each successive trio of dimples. Each successive trio of dimples may therefore be rotationally offset in either a clockwise or counterclockwise direction, as desired. It should be noted that embodiments of this type with successive dimple trios rotationally offset from the previous dimple trio by some angle is most effective when the heat exchanger tube comprises seamless tubing, thereby resulting in the least induced stress in the heat exchanger tube.

Referring now to FIG. 11, illustrated is a side elevation view of one embodiment of a heat exchanger tube 1100 constructed according to the principles of the present invention. The heat exchanger tube 1100 comprises first, second and third sections 1110, 1120, 1130, respectively. The first section 1110 is a substantially straight section for positioning the heat exchanger tube 1100 within a heat exchanger cabinet (not shown). The second section 1120 has a substantially U-shaped bend to re-route the heat exchanger tube 1100 to minimize horizontal cabinet size. The third section 1130 has five trios of dimples 1131-1135 impressed therein so as to create turbulent fluid flow through the heat exchanger tube 1100. One who is of skill in the art is familiar with such a heat exchanger tube and how it may be formed in general.

Specifically, the dimpled third section 1130 of the heat exchanger tube 1100 of FIG. 11 may be formed in a forming jig and hydraulic press. Referring now to FIG. 12, illustrated is a perspective view of one embodiment of a hydraulic dimpler 1200 for the manufacture of a heat exchanger tube constructed according to the principles of the present invention. The hydraulic dimpler 1200 comprises a two-piece part holder 1210, and first, second and third hydraulic rams 1221, 1222, 1223. One who is of skill in the art is familiar with hydraulic dimpling of tubing in general.

Referring now to FIG. 13 with continuing reference to FIG. 11, illustrated is an enlarged view of the part holder 1210 and a portion of the first, second and third hydraulic rams 1221, 1222, 1223 of FIG. 12. The first, second and third hydraulic rams 1221, 1222, 1223 have hemispherical end forming tools 1321, 1322, 1323 proximate the tube 1301 being formed. Dimple trios 1131-1135 may be impressed using the hydraulicly operated press forcing the three hemispherical end forming tools 1321, 1322, 1323 radially inward and spaced around the circumference of the tube 1100 at approximately 120° intervals while holding the tube 1100 motionless in the part holder 1210. One who is of skill in the art is familiar with this process. In one embodiment, a single trio may be formed at each time. In a preferred embodiment, all dimple trios 1131-1135 may be formed simultaneously by assembling a press that has an appropriate number of banks of hydraulic rams 1221, 1222, 1223. Rotational locating of successive dimple trios can be achieved by appropriately positioning each successive bank of hydraulic rams 1221, 1222, 1223.

Referring now to FIG. 14, illustrated is a heating system 1400 constructed according to the principles of the present invention. The heating system 1400 comprises a cabinet 1410, a frame 1420, a heat exchanger 1430 and at least one heat exchanger tube 1440. The heat exchanger tube 1440 is coupled to the frame 1420, and the frame 1420 is coupled to the cabinet 1410. A turbulating structure 1445 constructed according to the principles of the present invention is disposed within the heat exchanger tube 1440.

Thus, a heat exchanger apparatus has been described comprising a heat exchanger tube having turbulating structure in the form of trios of elements disposed within the heat exchanger tube. The advantages of the present invention include reducing residual stress within the heat exchanger tube while minimizing overall cabinet size and increased Reynolds number for flue products. The resultant increased pressure drop increases overall efficiency accordingly. An unobstructed path is also provided for the drain of condensate during off-season and off cycle operation.

Although the present invention has been described in detail, those skilled in the art should understand that they can make various changes, substitutions and alterations herein without departing from the spirit and scope of the invention in its broadest form. 

1. A heat exchanger apparatus, comprising: a frame; a tube coupled to said frame; and turbulating structure disposed within said tube and extending into an inner hollow space thereof for promoting turbulent fluid flow within said tube, said turbulating structure comprising elements located arcuately around an inner periphery of said tube at approximately 120° increments.
 2. The apparatus of claim 1 wherein said elements comprise dimples formed in said tube.
 3. The apparatus of claim 1 wherein said tube has a longitudinal axis and wherein said turbulating structure comprises a first dimple trio formed in said tube and having a first trio of centers, said first trio of centers substantially coplanar with a plane normal to said longitudinal axis.
 4. The apparatus of claim 3 wherein said turbulating structure comprises a second dimple trio spaced apart from said first dimple trio along said longitudinal axis, and wherein said tube has: a first reference radius from said longitudinal axis and through a center of one of said elements of said first dimple trio; and a second reference radius from said longitudinal axis and through a center of one of said elements of said second dimple trio; and wherein said first and second reference radii are coplanar.
 5. The apparatus of claim 4 wherein said first dimple trio has a first dimple depth and said second dimple trio has a second dimple depth not equal to said first dimple depth.
 6. The apparatus of claim 3 wherein said turbulating structure comprises a second dimple trio spaced apart from said first dimple trio along said longitudinal axis, and wherein said tube has: a first reference radius from said longitudinal axis and through a center of one of said elements of said first dimple trio; a second reference radius from said longitudinal axis and through a center of one of said elements of said second dimple trio; and wherein said first and second reference radii are non-coplanar.
 7. The apparatus of claim 6 wherein said second reference radius arcuately differs from said first reference radius by an angle between about ±5° and about ±30°.
 8. The apparatus of claim 7 wherein said turbulating structure comprises a third dimple trio spaced apart from said second dimple trio along said longitudinal axis, and wherein said tube has a third reference radius from said longitudinal axis and through a one of said elements of said third dimple trio wherein said third reference radius arcuately differs from said second reference radius by an angle between about ±5° and about ±30°.
 9. The apparatus of claim 1 wherein said turbulating structure comprise said dimples including smoothly curving surfaces in said tube.
 10. The apparatus of claim 1 wherein said tube has a weld parallel said longitudinal axis.
 11. The apparatus of claim 10 wherein a one of said elements is diametrically opposed said weld.
 12. The apparatus of claim 1 wherein said tube has a path for off-cycle or off-season condensate.
 13. A method of manufacturing a heat exchanger apparatus, comprising: providing a frame; coupling a tube to said frame; and disposing turbulating structure within said tube and extending into an inner hollow space thereof for promoting turbulent fluid flow within said tube, said turbulating structure comprising elements located arcuately around an inner periphery of said tube at approximately 120° increments.
 14. The method of claim 13 wherein disposing includes forming dimples in said tube.
 15. The method of claim 13 wherein said tube has a longitudinal axis and wherein disposing includes forming a first dimple trio in said tube, said first dimple trio substantially coplanar with a plane normal to said longitudinal axis.
 16. The method of claim 15 wherein disposing includes forming a second dimple trio spaced apart from said first dimple trio along said longitudinal axis, and wherein said tube has: a first reference radius from said longitudinal axis and through a one of said elements of said first dimple trio; and a second reference radius from said longitudinal axis and through a one of said elements of said second dimple trio; and wherein said first and second reference radii are coplanar.
 17. The method of claim 16 wherein disposing includes forming said first dimple trio having a first dimple depth and forming said second dimple trio having a second dimple depth not equal to said first dimple depth.
 18. The method of claim 15 wherein disposing includes forming a second dimple trio spaced apart from said first dimple trio along said longitudinal axis, and wherein said tube has: a first reference radius from said longitudinal axis and through a one of said elements of said first dimple trio; and a second reference radius from said longitudinal axis and through a one of said elements of said second dimple trio; and wherein said first and second reference radii are non-coplanar.
 19. The method of claim 16 wherein disposing includes forming said second dimple such that said second reference radius arcuately differs from said first reference radius by an angle between about ±5° and about ±30°.
 20. The method of claim 19 wherein disposing includes forming a third dimple trio spaced apart from said second dimple trio along said longitudinal axis, and wherein said tube has a third reference radius from said longitudinal axis and through a one of said elements of said third dimple trio wherein said third reference radius arcuately differs from said second reference radius by an angle between about ±5° and about ±30°.
 21. The method of claim 13 wherein disposing includes forming said dimples including smoothly curving surfaces in said tube.
 22. The method of claim 13 wherein coupling includes coupling a tube having a weld parallel said longitudinal axis.
 23. The method of claim 22 wherein coupling includes coupling wherein a one of said elements is diametrically opposed said weld.
 24. A heating system, comprising: a cabinet; a frame coupled to said cabinet; a heat exchanger having at least one tube coupled to said frame; and turbulating structure disposed within said tube and extending into an inner hollow space thereof for promoting turbulent fluid flow within said tube, said turbulating structure comprising elements located arcuately around an inner periphery of said tube at approximately 120° increments.
 25. The heating system of claim 24 wherein said elements comprise dimples formed in said tube.
 26. The heating system of claim 24 wherein said tube has a longitudinal axis and wherein said turbulating structure comprises a first dimple trio formed in said tube, said first dimple trio substantially coplanar with a plane normal to said longitudinal axis.
 27. The heating system of claim 26 wherein said turbulating structure comprises a second dimple trio spaced apart from said first dimple trio along said longitudinal axis, and wherein said tube has: a first reference radius from said longitudinal axis and through a one of said elements of said first dimple trio; a second reference radius from said longitudinal axis and through a one of said elements of said second dimple trio; and wherein said first and second reference radii are coplanar.
 28. The heating system of claim 27 wherein said first dimple trio has a first dimple depth and said second dimple trio has a second dimple depth not equal to said first dimple depth.
 29. The heating system of claim 26 wherein said turbulating structure comprises a second dimple trio spaced apart from said first dimple trio along said longitudinal axis, and wherein said tube has: a first reference radius from said longitudinal axis and through a one of said elements of said first dimple trio; a second reference radius from said longitudinal axis and through a one of said elements of said second dimple trio; and wherein said first and second reference radii are non-coplanar.
 30. The heating system of claim 29 wherein said second reference radius arcuately differs from said first reference radius by about +30°.
 31. The heating system of claim 30 wherein said turbulating structure comprises a third dimple trio spaced apart from said second dimple trio along said longitudinal axis, and wherein said tube has a third reference radius from said longitudinal axis and through a one of said elements of said third dimple trio wherein said third reference radius arcuately differs from said second reference radius by about −30°.
 32. The heating system of claim 24 wherein said turbulating structure comprises said dimples including curving surfaces in said tube.
 33. The heating system of claim 24 wherein said tube has a weld parallel said longitudinal axis.
 34. The heating system of claim 33 wherein a one of said elements is diametrically opposed said weld. 